The search for new thermostable polymers, thermosetting by addition reactions not releasing volatile compounds during the operation, gives rise to an increased interest in the manufacture of dense, homogeneous materials of low porosity.
To attain this object, cyano-addition reactions have already been used to cross-link fusible and soluble monomers or oligomers. As a matter of fact, these reactions occur upon mere heating of the reactants at the operating time.
Such cyano-addition reactions have been disclosed with aromatic, aliphatic or arylaliphatic compounds containing amide, imine, ether, sulfone, ketone and imide linkages. These reactions have been disclosed, for example, in the papers of Walton and Griffith, Applied Polymer Symposium, 1975,26,429, Polymer Science and Technology, 1975, 98, 665, and A.C.S. Division of Organic coatings and Plastic Chemistry, 1978 38, 596; of Keller and coll., SAMPE Quarterly, July 1981, p.1; and of Marullo and Snow, A.C.S. Symposium Series, 1982, vol.195, p.325.
Other examples of these reactions are given in U.S. Pat. Nos. 3,890,274, 3,996,196, 4,056,560, 4,057,569, 4,102,873, 4,116,945, 4,136,107, 4,209,458, 4,223,123, 4,234,712, and 4,238,601 and in the French patent application No. 2,568,257. From these works it appears that several problems remain unsolved concerning the operating conditions, the impact strength and the polymerization conditions.
For the operating conditions, the difficulties result mainly from the fact that the utilized products have melting or softening temperatures of at least 200.degree. C.
The impact strength of the finished products is generally rather low since the size of the segments between the end recurring units of phthalonitrile type is voluntarily reduced to keep the melting temperature as low as possible. It has been recently suggested in U.S. Pat. No. 4,409,382 to use flexibilizing segments essentially consisting of polyether-sulfone at variable polycondensation degrees in order to improve the impact strength.
For the polymerization conditions, it is known that the reaction of the phthalonitrile groups is very slow in the absence of metals or metal salts and that it is not very selective. For avoiding the use of metal compounds, Marullo and Snow (see above mentioned reference) and U.S. Pat. Nos. 4,408,035 and 4,410,676 have recommended conducting the polymerization reaction in the presence of phenols or of primary amines.
Under these conditions the gelation time is considerably shortened and the polymerization temperatures are lower. However, the structure of the so-formed polymers is not well defined and the by-products resulting from the conversion of these additives remain in the final material as unstable small molecules.
The above-mentioned French patent application discloses a new method for converting phthalonitrile groups to phthalocyanine macrorings having a very good thermal stability. This reaction has been observed on polyimide oligomers ending with ortho-dinitrile functional groups containing, in their macromolecule chain, aromatic rings interconnected with secondary alcohol (-CHOH-) groups. It has been shown that the formation of polyimide co-polyphthalocyanine lattices in these oligomers is inducted by an intramolecular oxidation-reduction of the benzhydrol groups.
The compositions mentioned in this patent application have excellent thermal properties but, for many applications, their melting temperature is too high and the operating conditions too severe.